I'm surprised owners of big tanks don't just do it experimentally: measure as they pump in (or out) known amounts of fluid. The oil delivery guy would kill me if I made him stop every 50 gallons (or whatever). My oil tank isn't shaped all that funny and I know the angle. I know it doesn't matter ultimately, but it sounds like fun. I also have to account for the axis of the float line not being quite vertical. I used to do a lot of computational geometry at a video game place I worked so this isn't so hard. Easiest is probably to just make a 3d model of the tank and do it numerically, turning the model into very thin horizontal slices. I can already feel the wheels turnin'. Yes, I admit what you've all suspected: I have no life.

Trying to figure it out if you couldn't verify the tank's exact shape or the angle it is buried at...now that sounds hard!!

: a psychological condition or a relationship in which a person is controlled or manipulated by another who is affected with a pathological condition (as an addiction to alcohol or heroin) ; broadly : dependence on the needs of or control by another

About the single float idea... You could use a float with one strong magnet on it to activate small magnetic switches, like these. That would take up less tank space and they are 2 for a buck.

That is a fantastic idea. I was put off by the tilting float switches a bit because of the need to run all the dangly wiring. And it's cheap. If I put a few magnets in the float I could arrange it so that one switch is always triggered (or just space more switches properly). Magnet doesn't even need to be inside the float as it can dangle beneath.

And they're from The Electronic Goldmine! Just the excuse to order from them I was looking for. Have to make the most of the shipping and handling charges, don't ya know.

: a psychological condition or a relationship in which a person is controlled or manipulated by another who is affected with a pathological condition (as an addiction to alcohol or heroin) ; broadly : dependence on the needs of or control by another

Unfortunately, he said it was a crawl space oil tank so I doubt seeing it will be that easy. However, he could do that and put the float in that external tube so if a switch ever needs replaced, needs adjusted, or breaks it isn't sitting inside the tank. Then it won't matter if the oil put in there is ever conductive too.

I did think of using one of those mower fuel caps that have the float and the gauge on them but that is very dependent on how deep the tank is.

I need to measure it (pain to get into the crawlspace). It's a sideways 275 gallon tank, so not too tall. Right now I have a clear tube off of a tee fitting, but to see it I use a camera. I considered a float system with a tall rod to get it upstairs (the room I want the indicator in is next door to the tank). I could still do that I guess. Need a good source for a clear pipe section. Let's see...the rod would have to be somewhere around 6 or 7 feet I guess to get it up to a convenient viewing height. That's pretty long. Need to be light or the float would have to be big.

My first attempt was using the trapped air in the tube and a manometer to measure the pressure changes but it didn't read consistently.

: a psychological condition or a relationship in which a person is controlled or manipulated by another who is affected with a pathological condition (as an addiction to alcohol or heroin) ; broadly : dependence on the needs of or control by another

If you were going to use a rod, there's probably no need to reinvent the wheel, just add a rod to this:

I imagine that a fiberglass rod like the kind used for driveway reflectors could do the job well but might be heavy. Else, if you could get a really long drinking straw, that would be lightweight and stiff enough (given that you use a pipe as a housing).

I guess I could join a couple rods together. Still seems heavy-ish. I like the idea of having an electronic one so it can flash when it gets low. That setup uses a lever to get the travel height down. Not that I couldn't use that as well.

Spent a minute listing all the approaches I could think of. Did I miss any?

: a psychological condition or a relationship in which a person is controlled or manipulated by another who is affected with a pathological condition (as an addiction to alcohol or heroin) ; broadly : dependence on the needs of or control by another

: a psychological condition or a relationship in which a person is controlled or manipulated by another who is affected with a pathological condition (as an addiction to alcohol or heroin) ; broadly : dependence on the needs of or control by another

: a psychological condition or a relationship in which a person is controlled or manipulated by another who is affected with a pathological condition (as an addiction to alcohol or heroin) ; broadly : dependence on the needs of or control by another